Process for removing electrically conductive coatings from ceramics



July 20, 1965 N. I. PERKINS 3,195,971

PROCESS FOR REMCVING ELECTRICALLY CONDUCT-IVE COATINGS FROM CERAMICS Filed Jan. 5, 1961 4o 26 ME EL 42 1 $4 3o ,2 \j;

NORRIS l. PERKINS I ENTOR.

ATORNE United States Patent 3,195 971 PROCESS FOR REMO'VEN G ELECTRHIALLY CON- DUQTIVE C(EATINGS FRUM CERAMECS Norris I. Perkins, Danvers, Mass, assignor to Sylvania Electric Products Inc, a corporation of Delaware Filed Jan. 5, 1961, Ser. No. 89,796 7 Claims. (Ci. 316-1) This invention rel-ates to the removal of portions of an electrically-conductive coating from a ceramic to which it has been applied. More specifically, the invention concerns the removal of a small portion of a conductive coating from relatively slender, elongated electroluminescent lamps.

Various methods have been used to prepare the conductive coating and various ceramics may be made conductive by these methods. The coating may be applied by spraying the ceramic with a solution of metal compounds, for example chlorides, oxides, sulfates or organic complexes of tin, antimony or indium; however, other successful methods of applying the coating have been, for example, dipping and vapor deposition If the ceramic is hot when the solution of metal compounds is sprayed, a metal oxide of the metal compound will be formed; however, the oxide of such compounds may be formed by subsequently heating a lamp which is coated while cold.

The method of removing the conductive film according to this invention is not limited to the method by which the coating of oxide is applied or formed nor to any particular ceramic. It may be used in a wide variety of applications where it is desirable to remove conductive coating from a ceramic surface thereby insulating the coating from the remainder of the surface.

One specific application of the conductive ceramic which requires an insulated area is the ceramic electroluminescent lamp which generally comprises a metal base, a layer of electroluminescent phosphor dispersed in a light-transmitting dielectric media and the previously-described light-transmitting, electrically conductive coating.

When varying or alternating voltage is applied between the conductive coating which serves as one electrode and a metal base which serves as another electrode, light will be emitted from interposed phosphor. Care must be exercised to insulate the conductive film from the metal base, since if contact occurs, the lamp will short circuit. This condition may be avoided by recessing the conductive coating on the face of the phosphor-dielectric layer thereby insulating the conductive layer from the metal base.

The recess or insulation has been obtained in previous methods by appropriately masking the lamp before the application of the conductive layer or by removing a portion of this layer after coating the entire lamp. Masking poses production problems since each lamp is individually handled and the results are not always satisfactory. The better method, then, is to remove portions of the conductive layer after it has been coated on the lamp, and such post-coating methods for removal of the conductive layer have included abrasion and chemical action. Abrasion is not always adequate since a substantial amount of time is consumed in individually grinding or sand blasting each lamp. Furthermore, the results are not always satisfactory since the optical properties of the lamp may be changed and also the treatment depends upon the skill of individual operators. Chemical action, such as treatment with sulphuric acid, is not always satisfactory since the method is quite tedious and time consuming.

An alternative method for removing the electricallyconductive layer depends upon electrolytic action, such as described in U.S. Patent to Butler et al. 2,722,511. This method, which has generally been accepted as satisfactory,

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includes partially immersing an electroluminescent lamp in an electrolyte and applying an electric current to the system, whereby the depth of lamp immersion will determine the area of conductive film removal. Although the method is quite satisfactory and efficient in treating lamps having large, generally fiat surfaces, difficulties are encountered when it is applied to relatively slender, elongated lamps. Labor costs are raised due to the constant checking of the electrolyte bath level, as required to insure a uniform amount of conductive film removal. Another difficulty encountered in the electrolytic method results from clamps which hold the elongated lamps during proc essing. These clamps will eventually contaminate the electrolyte due to chemical action and may even scrape the conductive coating, thereby damaging the lamp.

The method of removing the conductive coating or layer according to this invention has none of the difliculties encountered in the previously discussed methods and may be applied to both flat and relatively slender, elongated, ceramic lamps. Such treatment of the coated ceramic lamp involves heating a small portion of the ceramic to a temperature above its melting point, whereby the fusing will produce an interruption in continuity and absorption of the electrically-conductive layer, thus preventing short circuiting.

The general object of this invention is to remove certain portions of an electrically conductive coating from an electrically-conductive ceramic material.

Another object of this invention is to insulate a lighttransmitting electrically-conductive layer from other portions of an electroluminescent lamp.

A further object is to remove a small portion of the conductive coating from ceramic lamps, particularly those having relatively slender, elongated shapes.

Other objects will become apparent to those skilled in the art upon reading the following specification when taken in conjunction with the appended drawings in which:

FIGURE 1 is a side elevation view showing the relatively slender lamps positioned on an endless belt undergoing treatment to insulate areas in the electrically conductive layer.

FIGURE 2 is a top plan view of the conductive film removal equipment, showing in particular the position of an adjustable battery of tipping burners.

FIGURE 3 is an enlarged detailed cross section view taken along the lines 33 of FIGURE 2. This figure shows the tipping burners fusing the ceramic and thus removing a portion of the conductive film from an electroluminescent lamp.

FIGURE 4 is an enlarged detailed view of an elongated relatively slender electroluminescent lamp having certain portions cutaway to show the various layers.

In each of the figures of the drawing similar numerical designations will connote similar elements.

According to this invention, ceramic electroluminescent lamps are placed between the series of gas fed tipping burners which are designed to develop extremely sharp pointed flames. When the flames contact the lamps, the ceramic will fuse, thereby breaking the continuity of the adjacent coated layer of electrically conductive light transmitting material and causing an adsorption of the electrically conductive materials in the melt. Upon cooling, the ceramic will harden and the electrically conductive layer will be electrically insulated from other areas of the lamp. The flame temperature is quite important in the process and must be maintained sufficiently high to raise the ceramic to above its melting point, but sufficiently low to avoid burning through the ceramic layers and the base metal which would, of course, destrol the lamp.

Referring to FIGURE 1, an endless belt 10 positioned between driving wheels 12 carries a plurality'of clamps- 14. In order .to use clamps efiiciently, it is generally although glass which has been rendered electrically connecessary to assemble the lamps in a gang 22, which.

comprises base strap26 and a plurality of vertically up The ganged lamps22 may then be placed in the clamps 14 as a standing lamps 24 spot'welded thereto.

unit; To eliminate difierences in conductive coating removal from one side of a lamp to another, it is gen- Cit erally essential to place the lamp equidistantly between opposing batteries of tipping burners 28. After passage 7 through the battery of burners 28, the lamps are allowed to cool, thereby resolidifying the melted ceramic. Thus,

when the operator removes a gang of lamps from the" on the belt 10, so that the'lamps will be equidistantly spaced between the two batteries of tipping burners '(only one battery of which is shown in this figure). The burners are adjustably mounted on a vertical stand 4%, which ductive may also be usedin some cases.

7 7 When desired, a layer of ceramic dielectric material 54 can be coated and fused to the rod53 to serve as a bonding surface'for the light-producing, ceramic dielectric-electroluminescent phosphor layer 55.

' An example of electroluminescent phosphors suitable for use inthe light-producing layer 55 is copper-activated zinc sulfide such as described in the co-pending Goldberget al. application entitled Electroluminescent Device, Serial No; 714,481,:filed February ll, '1958, 'Patent No. 7 Generally, such phosphors are dispersed in afusible light-transmitting glass dielectric such as shown in the co-pe'nding' application of Richard M. Rulon,

Serial No. 365,617, filed July 2; 1953, now abandoned.

Directly over the ceramic-phosphor layer 55 is a lighttransmittihg electricallyfconductive layer 56, 59 (which is inturn is rigidlymounted on a horizontally adjustable base 42. The base 42 may then be mounted'on a suitable table 15., Other adjustable mountings are possible, for example, the entire adjustable burner assembly .may

be suspended above the belt, thereby affording a bit more ease in adjustment. a V, I a V 7 FIGURE 2 further illustrates the positioning of the lamps 24 between the opposing batteries of tipping burners 28. Each battery may comprise a plurality of burners 32 and although four are shown more or less may be used.

A gas and oxygen mixture enters mix-ing cylinder 34.

through inlet hose 35 and passes 'throughburners 32 to burn in sharp, pointed flames. These flames contact lamps 24 at any desired longitudinallocation and develop sufl'lcient heat to fuse the ceramic. 4 V

Adjustment of the-distance between opposing the batteries of burners is obtained by loosening nut 46 so that stand 42 may movein tracks 48. The adjustment of stand 42 will control, together with the flame temperature, the'area and depth of ceramic insing. For example, ifonly the tips of the flame touch the lamps 24,

only a small portion ofthe ceramic will be melted and thus only a small portion of theconductive film absorbed therein and removed. If, however, the wider portions of the flame contact-the lamp, larger fused'areaswill be obtained. 7

A vertical adjustment of the burners will allow accommodation for difierences in various coatingheights and the positioning of a fusedlportionSd. Such vertical ad- I justment may be obtained by loosening turnserew 45 and moving the battery of burners 28. to the desiredheight.

The details of the ceramic fusing and-concurrent conductive film removal operation are shown in FIGURE 3.-

The vertically standing lamp 24, positioned in belt-mount ed clamp 14, passes transversely between the dances of opposing burners 32. When the flame strikes the portion 58 of. the lamp, a ceramic layer will melt and the continuity'of the adjacent'conductive film will be broken;

Suitable clamps for holding the lamps comprise two L- shaped members 16. Outwardly curved portions 29, which are prolongations of the upright legs 16 are spring biased toward" each other to providesuitable gripping for the, ganged 1amps22. When a gang of lamps is placed in clamps 14, and passed through the flames, a uniform conductive layer removal from each lamp will be obtained since the belt 10 is maintained at a constant velocity.

The ceramic electroluminescent;lamp having a series of layer is shown in FIGURE 4; Serving as the base and one electrode inthe lamp is the metal rod or tube 53,

electrodes must be insulated from each other; lation according to this invention is providedby the band steps in their fabrication.

indicated by two numericaldesignations since one portion is insulated from the other po rtion, although each one is identical in composition); Methods applicable for producing this layer are those commonly used for mak- 1 ing various ceramics electrically conductive and may include spraying a hot lamp with asolution of metal compounds, for example stannous chloride in formaldehyde.

Ofcourse, other methods for producing this layer 56,- 59

and other metal compounds have applicability, for example,,the;vapor deposition or dipping of antimony or indium oxides, sulfates or' organic complexes may be used.

' The entire lamp is. then coated with a layer of transparent glass 57 which whenifused protects the transparent conductive coating 56 from accidental removal and the efiects ofhumidity. 1 r v p j v 'Irrespective'of the manner of applying the electrically conductive, light-transmitting electrode 56, 59 and irrespective of'the care taken in its application, mass pro- .duction methodso'ften produce a lamp which has an inherent shortcircuit. The'electrode comprising electrical- 1y conductive layer 56, 59 may contact the other electrode comprising metal rod 53 and therefore to prevent a short circuit when the lamp is connected to a power supply, the

The insu- 58 on the lamp 24. V a

It is possible jtoatreat the ceramicelectroluminescent lamps accordingto this invention after either of two treated immediately after the application of conductive layer 56,. 59 whereby 'the flames will contact the lamp '24 Iandmelt the ceramic dielectric-phosphor layer 55. Since the electrically conductive layer 56, 59 is coated on this. dielectric-phosphor layer 55,1 melting thereof. will cause conductive film portion 56 to separate from conductive film portion 59. I I I The lamps may also be treated after the light-transmitting protectiveglass layer 57 has been applied. In this case, when the flames contact the lamps, the protective glass layer will tuse and since it is coated over electrically conductive layer 56, 59, the fusing will cause conductive layer portion 56 to se'paratepfrom' conductive layer portion 59, thus producing aninterruption in continuityand insulating the conductive film portion 56 from the remainder of the lamp; It is usually immaterial ifthe flame penetrates the lamp and if more than one layer of the ceramic coating is melted, since in all cases the requisite insulation may be obtained. e I

When ,the. lamp is placed in service, one electrical contact is placed on metal rod 53 .and another on isolated electrically conductive layer portion .56. The area of theconductive layer isolated from the metal determines the light-emitting portion of the lamp; There-. ,fore the area of light emission may be varied by changing the location of theband 58. Such variation may be obtained by adjustingthe vertical positioning of the battery of tipping burners 28.

In one case the lamp may be Although what has been shown and described constitutes a preferred embodiment of the present invention, various changes and modifications will suggest themselves to those skilled in the art upon reading the foregoing specification. The invention, therefore, should not be limited to the exact details shown, but only by the spirit and scope of the appended claims.

I claim as my invention:

1. The method of treating a light transmitting ceramic material having an adhering electrically conductive coating of metal oxide, the steps comprising: heating a portion of said light transmitting ceramic to a temperature above its melting point, thus fusing said ceramic to break the continuity of said conductive layer of metal oxide, and then cooling said fused portion to resolidify said ceramic and obtain electrical insulation.

2. The method of treating a light-transmitting, ceramic material having an adhering, light-transmitting, electrically conductive coating of metal oxide, the steps comprising: heating a portion of said ceramic to a temperature above its melting point, thus fusing said ceramic and breaking the continuity of said conductive layer of metal oxide, and then cooling said fused portion to resolidify said ceramic and obtain electrical insulation.

3. The method of treating an electroluminescent lamp having an electroluminescent phosphor dispersed in a light-transmitting ceramic dielectric and having an adhering light-transmitting electrically conductive coating of metal oxide to electrically insulate areas of the conductive layer from the lamp comprising: heating a portion of said ceramic to a temperature above its melting point, thus fusing said ceramic and breaking the continuity of said adhering conductive coating of metal oxide, and then cooling said fused portion to resolidify said ceramic and obtain electrical insulation.

4. The method of treating a ceramic electroluminescent lamp having an electrolumenescent phosphor dispersed in a light transmitting dielectric and having an electrode comprising an adhering light-transmitting, electrically conductive layer of metal oxide, the steps for electrically insulating areas of the conductive layer from the lamp comprising: heating a portion of the ceramic of said electroluminescent lamp to a temperature above its melting point, thus fusing said ceramic and absorbing the adhering electrically conductive layer of. metal oxide in the melt and then cooling said fused portion to resolidify the ceramic and obtain electrical insulation.

5. A method of treating a ceramic electroluminescent 6 lamp having an electroluminescent phosphor dispersed in a transparent dielectric and having an electrode comprising an adhering light-transmitting, electrically conductive layer of metal oxide, the steps for electrically insulating areas of the conductive layer from the rest of the lamp comprising: heating a portion of the ceramic of said electroluminescent lamp to a temperature above its melting point by exposing said ceramic to flames, thus fusing said ceramic and absorbing the adhering electrically conductive layer of metal oxide in the melt, and then cooling said fused portion to resolidify the ceramic and obtain electrical insulation.

6. The method of treating relatively slender elongated ceramic electroluminescent lamps having electroluminescent phosphor dispersed in a transparent dielectric and having an electrode comprising an adhering light-transmitting, electrically conductive layer of metal oxide, the steps for electrically insulating areas of the conductive layer from the rest of the lamp comprising: heating a portion of the ceramic of said electroluminescent lamp to a temperature above its melting point by exposing said ceramic to flames, thus fusing said ceramic and absorbing the adhering electrically conductive layer of metal oxide in the melt, and then cooling said fused portion to resolidify the ceramic and obtain electrical insulation.

7. The method of treating relatively slender, elongated, ceramic electroluminescent lamps having an electroluminescent phosphor dispersed in a dielectric and having an electrode comprising an adhering, light-transmitting electrically conductive layer of metal oxide, the steps for electrically insulating areas of said conductive coating from the remainder of the lamp comprising: heating a portion of the ceramic of said electroluminescent lamp to a temperature above its melting point by contacting said ceramic with flames, thus fusing said ceramic and absorbing the adhering electrically conductive layer of metal oxide in the melt and then cooling said fused portion to resolidify the ceramic and obtain electrical insulation.

References Cited by the Examiner UNITED STATES PATENTS 2,178,232 10/39 Hickok 29 2s.17x 3,003,904 10/61 Riggen 15689X RICHARD H. EANES, 11L, Primary Examiner.

LEON PEAR, Examiner. 

7. THE METHOD OF TREATING RELATIVELY SLENDER, ELONGATED, CERAMIC ELECTROLUMINESCENT LAMPS HAVING AN ELECTROLUMINESCENT PHOSPHOR DISPERSED IN A DIELECTRIC AND HAVING AN ELECTRODE COMPRISING AN ADHERING, LIGHT-TRANSMITTING ELECTRICALLY CONDUCTIVE LAYER OF METAL OXIDE, THE STEPS FOR ELECTRICALLY INSULATING AREAS OF SAID CONDUCTIVE COATING FROM THE REMAINDER OF THE LAMP COMPRISING: HEATING A PORTION OF THE CERAMIC OF SAID ELECTROLUMINESCENT LAMP TO A TEMPERATURE ABOVE ITS MELTING POINT BY CONTACTING 